09:05:32 Great, okay, right. So thank you very much for asking me to give this tutorial on this concept of Barry on clearing.
09:05:41 So we just had a great talk from Elisa about essentially quenching of satellites in large scale cosmological simulations, and I'm going to be talking more about the picture for central galaxies and cosmological simulations.
09:05:56 So I want to start with this. Now, somewhat legendary image that we all love to show in our talks.
09:06:03 And I'm including it because I think it gives a really good impression of how galaxy formation is a self regulating process so you have to have some balance between gassing flows and start guess, either forming stars or ending up in gas outflows, and
09:06:23 have to have this happening because otherwise you either over call and form too many stars, or you don't form enough. And something that crystal Martin touched on in her talk yesterday with our lovely bathtub images, is that the CGM is of course going
09:06:31 to be vital to this self regulation process.
09:06:35 But what I actually want to talk about today is how you can disrupt this self regulation, and the role that the CGM plays in that. And you have to disrupt the self regulation somehow if you want to produce the quench galaxy population.
09:06:50 And most importantly, if you want to quench galaxies and keep them quenched so it's not enough to just remove the RSM and remove the fuel for star formation you also have to stop inflows from the CGM from essentially reigniting star formation in that
09:07:05 galaxy.
09:07:06 And so the key ingredient for all of this, at least in the simulations I look at is this hidden ingredients on the right hand side of this equation. And that's the growth of the supermassive black hole.
09:07:18 So how might you go about disrupting this whole self regulation picture.
09:07:23 So in law my systems, while they're merrily start forming.
09:07:28 You can think of it as the process of getting gas away from the center with stellar.
09:07:35 The star formation driven outflows essentially. So in this nice plot by Ben Keller, which is the entropy versus radius, you can imagine, Stella feedback essentially inflating high entropy bubbles of gas in the center of the system.
09:07:49 And then these can kind of buoyant Lee floats out into the CGM, and then they may leave all together, or they may relatively cool back down and replenish the interstellar medium again in fountain flow.
09:08:03 But as you start to form a hot Halo and more massive systems this whole process starts to become much less effective, and it gets to the point. And this was nicely shown by some members of the eagle team.
09:08:16 A couple of years ago. Once you start approaching halos of massive about 10 to the 12 so the masses, the entropy of the halo has reached such a point that it's really higher than the entropy of the outflow and gas, driven by star formation feedback.
09:08:32 And so, suddenly you get this very rapid buildup of gas at the halo center that can't be regulated by Stella outflows anymore.
09:08:41 And so all this gas has to do something and it eventually fuels. The rapid growth of the central black hole in the system.
09:08:49 And of course when a black hole grows rapidly, it has to inject Ag and feedback.
09:08:54 And what we find and I think this figure from a recent paper by Ben shows nicely.
09:09:00 That I mean this is an example for Eagle, what you find is that when the black holes grow rapidly and the systems that are, that have reached this critical point.
09:09:10 The overall contents of the CGM decreases in response to this rapid injection of Ag and feedback. And so this is what I'm turning Barry on clearing, I don't have a better name for it yet, but really I'm talking about the clearing outs of the, the contents
09:09:27 of the CGM itself by AJ and feedback.
09:09:31 And this is something that I've seen across many of the kind of flagship large scale simulations of the day.
09:09:38 So these figures from Eagle from illustrious tng Simba horizon AGM, and they all show roughly the same thing which is the contents of the CGM f CGM versus halen mass.
09:09:52 And what we see at this critical Halo mass scale about 10 to the 1210 to the 12.5 solar masses, is that there is the gas content of the CGM of Central galaxies is severely suppressed relative to the cosmic coverage.
09:10:09 And so what's doing this damage here is the integrated growth of the black hole.
09:10:14 So it's the, the amount of energy that's been efficiently coupled to the CGM over the system's lifetime. And this is quite nicely wrapped up in the black hole mass as a parameter, which is the coloring of these upper figures here from eagle and T and
09:10:30 And you can see that at this kind of mass scale here. The, the systems with the most massive black holes in the fixed mass these red points or read or points here and tangy of those which hosts the most gas pour CGM, essentially.
09:10:48 So, this is what we're calling barium clearing.
09:10:51 And it's actually something that seems to be required in these simulations to produce the quenched galaxy population.
09:11:00 So yes, what I just said. So, this spiral clearing process does appear to be facilitating quenching, and this is where we get down to this whole theme that we have this week of how the CGM impacts galaxy evolution.
09:11:12 So this is the same kind of figure I was showing in the previous slide of the gas contents of the CGM versus halen us.
09:11:20 But now I'm coloring essentially by the specific star formation rates of the galaxies at the centers of these halos.
09:11:27 And what you can see very clearly in both eagle and tng is that the most gas poor systems which has the most over massive black holes are the ones that almost universally host quenched or very low star forming galaxies, whereas gas rich halos tend to
09:11:44 host actively start forming galaxies.
09:11:49 And so this is quite complimentary to the sort of general results from all the different simulations, so there's a nice figure from Abu zR town that kind of wraps this up.
09:11:59 If you look at Black Hole mass versus stellar mass and color it by the specific star formation rate of the galaxy, you see that the systems with the most over massive black holes are almost always quenched across many different simulations.
09:12:14 And this is also supported by some observations. So, of course, black hole masses are very difficult to dynamically determined there are only about 100 or so systems for which there are dynamically measured black Congress's, and this work from Brian Carruthers
09:12:29 really clearly shows that the systems that have the most over massive black holes are the ones that tend to be quenched.
09:12:39 And so the reason this happens is that this whole process of barium clearing is a preventative process. So as well as just ejecting the material from the galaxy itself, and from the halo itself.
09:12:50 You're also preventing what's left in the CGM from cooling and fueling star formation in the central galaxy. And we can see this really nicely the simulations like equal and tng.
09:13:03 If we look at the specific star formation rate as a function of Halo mass, we can see that all these quench systems at the bottom here are those which have particularly long CGM cooling times, which is what the coloring represents here, and recent work
09:13:19 from the tangi team from Zynga tell show that this is a stronger effect or a smaller radius, essentially, so the inner CGM is is more strongly affected, in terms of this whole prevention of cooling.
09:13:35 So, if this is just entropy versus specific star formation right.
09:13:40 And you can see that the most quenched galaxies.
09:13:43 The CGM entropy is higher, and that this is a stronger slope here for the inner CGM, and for the gas right near the central galaxy.
09:13:52 So by clearing out your CGM you're essentially holding the replenishment of your isn.
09:13:58 And there's a nice complimentary idea here from Mark votes recent paper in that if you reduce the pressure of the CGM you allow residual star formation driven feedback to sweep out towards the left of the interstellar medium.
09:14:12 So that's a nice complementary idea.
09:14:15 So all this is about connecting quenching to the properties of the CGM through a Gen feedback.
09:14:22 But if you remember from towards the beginning of the talk, I said that this tends to happen at a critical mass.
09:14:29 So one might then ask, why is there such a diversity of fixed Halo mass, you know, why don't you just reach this critical point where you found a hot Halo and clear out your CGM.
09:14:41 So this is where we can really get down to the origin of this process and maybe from the origin of the quenching of Central galaxies really.
09:14:50 And what I want to convince you of over the next few minutes, is that this is the result of differences in the intrinsic properties of the Dark Matter Halo itself, most specifically in its assembly history, which correlates very strongly with how concentrated
09:15:04 or tightly bound the Halo is.
09:15:07 And this is something that's just purely set by cosmology by the initial conditions of the universe.
09:15:14 Okay, so I could show you this.
09:15:17 Using correlations in large scale volumes like I've been doing so far but actually a much more satisfying and beautiful way of showing this is by doing a more controlled galaxy formation experiment and so we can do this using this genetic modification
09:15:30 techniques that was pioneered at UCL.
09:15:33 And what it allows us to do is essentially take a patient zero galaxy so to speak and organic galaxy, which is a star forming desk in Eagle.
09:15:45 And so here's the halo master creation history of such a galaxy. And what we can do is essentially, turn the knobs on galaxy formation, so to speak, we make small changes to the initial conditions of the simulation, such that the system either forms earlier
09:16:03 or later. And so we ended up with the same final Halo mass. And this is the same system in the same large scale environment, but it collapses that earlier or later times, so we get a nice controlled experiment here.
09:16:17 And it turns out the impact of changing the assembly history of the Halo is really dramatic.
09:16:22 So if we take a look at how the black hole grows with time and each of these systems, we find that the earlier assembling case here, and I'll talk about all the shading is in a sec.
09:16:33 The earlier assembling case here, not only forms it's black hole. Earlier, because it forms it's hot Halo earlier, but it forms a massive black hole as well.
09:16:42 And similarly, if you dial the assembly to later time she former less massive black hole.
09:16:48 And this happens because more earlier assemblies things are more tightly concentrated.
09:16:54 And this makes this whole process of self regulating the formation of the galaxy much less efficient, and the black hole has to inject more energy into this more tightly bound system to compensate essentially.
09:17:06 So you end up with a more massive black hole in the injection of more energy and feedback.
09:17:11 So the shading here is that there's actually nine realizations of each of these histories, and we do this because the feedback in Eagle is stochastic.
09:17:20 So you just need to, if you're looking at one system you have to re simulate a bunch of times to get the real answer essentially.
09:17:27 Okay, so what happens to the, to the system so there's a lot of plots here but I'll just give you the highlights. So this earlier assembling system, which has formed a more massive black hole objects more of it CGM than the organic galaxy.
09:17:42 So you get this really clear difference in their final CGM content just by dialing back and forward the assembly history.
09:17:50 And the effects on the central galaxy and just as dramatic. So because of this preventative effective very on clearing, we find that while the organic galaxy is nice and Marilee start forming at the present day.
09:18:02 Almost every realization so there's some stochastic it here but almost every realization of the earlier assembling system that's been more strongly cleared of aspirins is quenched.
09:18:12 And so here are some pictures of the final galaxies that you get. And you can see that we've taken this star forming desk and turned it into a quenched elliptical just by dialing up and down this barrier and clearing process.
09:18:26 And so all these kind of trends also hold true and large volume simulations.
09:18:31 So I think there's something really profound here that you can connect the properties of galaxies, to the really intrinsic pure properties of the halo itself just through this interaction between feedback and the CGM.
09:18:47 So I'm going to tell him my thoughts to something more observational now in the last few minutes which I hopefully have, and just talk about.
09:19:02 Yeah, what was I gonna say, Yes, so I'm really pleased to say that these ideas of rejecting the CGM cup potentially being involved in quenching are picking up some speed within the question community itself.
09:19:07 So just a couple of headline results from from these teams so this paper, look at how they find actually that the best predictor of whether a galaxy in SPSS manga is quenched is the velocity dispersion at the center of the galaxy itself which of course
09:19:26 correlates wonderfully with the black hole mass. So more so than Hello mass Stella mass, any other parameter, they find that it's the velocity dispersion.
09:19:36 That is the best indicator of quenching.
09:19:40 And so similarly, I actually just two hours ago was listening to a talk by Sunday Faber about this paper.
09:19:46 So this paper by Zhu Chen, they built this time model for quenching that requires that the black hole is in effectively coupled four times the CGM binding energy to its surroundings.
09:20:00 In order to quench galaxies, and they find that this toy model, very nicely and cleanly separates star forming and quenched galaxies in the candles fields.
09:20:11 So these ideas of clearing the CGM are really picking up some speed.
09:20:16 So now just in the last few minutes I'll talk about ways in which we could go about observing this, so I'm slightly out of my wheelhouse here so I'd love to hear what the, the real observers, think about this afterwards.
09:20:30 But yeah, just start with absorption, which of course will have to do.
09:20:36 So Ben showed in a paper that we did last year that you can use the covering fractions of absorbers such as carbon four is a nice proxy for the CGM mass fraction, and in Eagle we find that there's a really nice anti correlation in a narrow Halo mass window
09:20:54 between the black hole mass, and the covering fractions of absorb as such as carbon for.
09:21:00 But there are some difficulties in the interpretation of something like this if you were to go and do these observations. So, primarily there's this issue that agent feedback can actually briefly and rich the CGM with these ions before these ions ultimately
09:21:14 become reflective of having having evacuated the CGM.
09:21:19 So in this platform bang you can see in Eagle that things like carbon four and six. They actually jump up after the growth of the black hole and then they drop down, and this is something that's also seen in Zoom's.
09:21:33 So this work by Nicole Sanchez shows, again using genetic modification that the current densities of oh six are actually higher in simulations with black hole feedback than without.
09:21:47 So some difficulties in using these absorbers as a proxy for a CGM here.
09:21:53 So moving on to a mission. So, as we all know, doing detailed studies using the X ray luminosity as a proxy for the CGI mass fraction or bit beyond our reach for Milky Way my systems at the moment, we kind of waiting for Athena and links for that.
09:22:10 But all of the simulations are kind of predicting quite nicely now that the systems that are actively start forming and haven't cleared their CGM have systematically X ray brights halos, and this is an eagle into n g, and in December.
09:22:26 So that's one potential route in the future for something that's more eminently feasible is actually using ears eater observations. So this is, again, I'm really plugging Ben's stuff here but so so this is something we worked on last year.
09:22:42 And essentially what you can do is you can use all these wonderful tools like pie XM and socks, etc that john z home and his collaborators have developed some like really realistic mock observations Maki resistor observations and simulations such as evil
09:22:59 and tng, and what they show if you stuck them up about the coordinates of star forming or crunch galaxy samples, is that there's a really clear difference between these two in terms of in terms of these mock observations.
09:23:12 And it turns out that these differences and X ray surface brightness between highly start forming so the solid lines and quenched in these dashed lines should be detectable once heroes eater is completed its survey.
09:23:29 So that's something that's a more eminently usable proxy for the CGM mass fraction around the systems.
09:23:37 So I think I've probably had my time, but I'll just wrap up by returning to this whole idea of connecting the fundamental intrinsic properties of halos to quenching through this barrier and clearing and just kind of real off this whole connection here.
09:23:54 Using these nice images of those genetically modified galaxies guide. So if you formerly, you tend to film a more over massive black hole in your Galaxy center.
09:24:05 And this clears your CGM more completely elevating it's cooling time. And so you're much more likely to host a quenched steroidal galaxy than in the system which forms later.
09:24:16 And I think this kind of connection between cosmology and the properties of galaxies. I don't know, for me the number one reason to study the CGM is connecting the dots of galaxy formation.
09:24:29 And with that, I'll thank you for your time.
09:24:33 Thank you john that was, that was great and it was, you know, you went 20 minutes so we have five minutes for questions.
09:24:41 And I will look for hands.
09:24:48 Otherwise, Okay, here we go. Corral, how would you go first.
09:24:57 I guess.
09:24:59 Um quick question is around my hand. Right. So, is there, right.
09:25:07 Clearly Black holes are a good mechanism for explaining the result of the difference in assembly history.
09:25:15 But are there other right basically Could it be that you know, the black holes and the CGM.
09:25:23 The differences in the CGM properties that they are both caused by something basically that, you know, the booth caused by the differences in assembly history, but not in a directly connected way.
09:25:36 Like, it seems like it's a, you know, it seems like that cause very good explanation for the connection, but are there other potential mechanisms.
09:25:50 Um, well, if you can simply say, for example, if there are differences in the environment of the Halo, depending on forms right like this idea of the genetic modification thing is that the environments that the Halo is identical.
09:26:04 Because it's the same system in the same environment and all you've done is just tweak the evidence to field right at the start of the simulation, such that the system overall forms in different times.
09:26:19 And you can be sure that it's the black hole that's doing the damage, because if you just simply run a simulation where you don't include black hole feedback.
09:26:27 All of these lovely trends that we see completely disappear.
09:26:32 So in, in this whole scenario we're finding of course the earliest among systems, they're more tightly bound to that but they actually hold on to less stuff.
09:26:40 And that's because of the black hole, and so if you take the black hole out, they hold on to more like you might expect.
09:26:46 So it's really the key really this is Adrian driven barium clearing to connecting the dots here.
09:26:54 Okay.
09:26:57 Thank you. Our next question about, about the X ray predictions which I guess been led but I'm asking you.
09:27:06 So, so how do you know for sure that when you find this in observations that it's because there's less mass rather than that the gas that is there very dense has been heated by more feedback.
09:27:22 Do you see what I mean so the star formation. Putting it like heating the gas around it could also elevate the, the X ray honesty.
09:27:32 Yeah, absolutely. Yeah, so I actually spent the first couple of my couple of years of my PhD worrying about that question before I turned my thoughts on to this sort of thing.
09:27:41 So yeah absolutely stuff that's been recently heated by supernova feedback is going to be very dense very metal enriched and it will dominate the X ray mission around individual systems.
09:27:52 And that's a lot of the cause for if I could just wind back. This scattering in Eagle, like all of these guys that are the most actually almost all of their mission is coming from this feedback heated stuff.
09:28:03 So it's not really very representative of the contents of the CGM, but I guess you would hope that in a stack, if you are stacking new Rosita maps up, you would somehow wash out a fair bit of that, you know, of that phenomenon, and ideally get to the
09:28:20 real underlying correlation with just using it as a proxy for the contents of the CGM be yeah that would be a problem that you'd have to think about
09:28:31 We haven't 90 seconds left. So Mark, very quick question and maybe you finished it in the breakout room
09:28:39 unmute Ernie, I just want to mention that, you know, I put in the chat I think you, but the black hole mass is actually responding to the central depth of the potential.
09:28:52 And so, I, you know, it's, it's not necessarily just the black hole mass is the primary cause the depth of the central potential is determined by how early it forums, which then increases the requirement to have a central black hole, which then does the
09:29:08 very unclear thing. So this went back to the question about, you know, could there be a common origin, that precedes the massive black hole I think the answer is yes.
09:29:19 Yeah.
09:29:22 Yeah. I mean, um, yeah, you're right.
09:29:26 I don't really know how to, how to respond to that other than to say yes, absolutely. I mean they they seem all of this seems very complimentary and the, the overall Halo concentration is really what setting it all.
09:29:40 Whether that's the very, the depth of the potential right at the center, which then, of course, determines your black holes properties, then what we should play say is, let's take it to the breakout room, go into breakout room.